When there is a speed change operation in a motorcycle, particularly at the time of an upshift, a clutch operation is generally performed to smoothly disengage a dog clutch of the transmission, that is, to disengage a speed change clutch.
However, it is known that in a case where a quick speed change operation is desired, particularly in a case of a race-specification vehicle or the like, the output of an internal combustion engine is decreased without a clutch operation being performed, and a torque transmitted to a transmission is thereby reduced to enable smooth changing of a speed change stage (see, for example, Patent Document 1).